Some of John Paulson's clients are indicating they may withdraw money from the billionaire's hedge fund firm, after it was involved in a transaction that led the U.S. government to file a lawsuit against Goldman Sachs Group Inc , The Wall Street Journal said.

Paulson has gone on the offensive to reassure investors his firm will remain unscathed, the newspaper said in its April 21 edition, citing the firm's Monday conference call with about 100 investors and a letter issued Tuesday night.

A call to Paulson was not immediately returned.

The U.S. Securities and Exchange Commission on Friday filed a civil fraud lawsuit against Goldman, alleging that the bank failed to tell clients that complex mortgage-related securities they were buying had been created by Paulson, who stood to benefit if the securities lost value.

Paulson was not charged in the SEC lawsuit.

According to the newspaper, investors are concerned that scrutiny over the Paulson firm's dealings may spread, including to non-U.S. regulators, and want to protect themselves in case new information surfaces, or the legal case distracts Paulson.

One investor said most of the people on the conference call were supportive, while another said there is no rush for the doors, the newspaper said.

Citing people familiar with the Monday call, the newspaper said Paulson's firm was asked whether he or anyone at the firm had received a Wells notice indicating possible civil charges. Paulson said no, the newspaper said.

Meanwhile, in the letter to investors, Paulson reportedly said that in 2007 his firm was not viewed as an experienced mortgage investor, and that many of the most sophisticated investors in the world were more than willing to bet against us.

Paulson's firm has a deadline next Friday for investors who want to withdraw money on June 30, the newspaper said.

Separately, according to the newspaper, the $7 billion hedge fund firm Magnetar Capital LLC also is moving to reassure investors that its mortgage-linked investment strategy was sound and can also withstand regulatory scrutiny.

A Magnetar representative could not immediately be reached for comment.

(Reporting by Jonathan Stempel; editing by Carol Bishopric)

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